Obama must find the best bad option in Syria

Having vowed that any use of chemical weapons by Syria would cross a U.S. "red line" and provoke a strong American response "with enormous consequences," President Barack Obama now finds himself under increasing pressure to act, following reports by U.S. and foreign intelligence agencies that the regime of President Bashar Assad used deadly sarin gas against opponents last year. The problem for Mr. Obama is that the military options for enforcing his promise range from bad to very bad — while the risks of doing nothing may be even worse.

Over the weekend, Republican Sens. John McCain of Arizona and Lindsey Graham of South Carolina suggested it would be relatively easy to ground Syria's air force with cruise missile attacks on military airfields. That would allow the U.S., Britain and France to set up a no-fly zone over the country to protect Syrian rebels from government air attacks, as was done in Libya, and also facilitate the creation of opposition safe havens inside the country along Syria's border with Turkey. Coupled with arming Syria's non-Islamist rebel factions, they said, a decisive U.S. military intervention in the country's two-year civil war could quickly lead to the fall of the regime and the emergence of a new, democratic government friendly to the West.

But that rosy scenario doesn't take into account the huge risks involved in using air power to dislodge Mr. Assad. In recent years, Mr. Assad has built up one of the most sophisticated air defense systems in the world with the help of Russian aid. Grounding Syria's air force would be far more difficult than knocking out Libya's, and even if Syrian planes were prevented from taking off, the government still has thousands of fixed and mobile surface-to-air missiles that would pose a deadly threat to allied aircraft.

Similarly, arming Syria's notoriously fractious and disorganized rebels could be a lot harder than it sounds. Over the last two years, Islamist factions affiliated with al-Qaida have emerged as the strongest rebel groups, and there's no assurance that weapons given to more moderate factions wouldn't end up in the hands of extremists. The U.S. could find itself supplying arms to the very people who would one day use those weapons against us.

The diplomatic obstacles to intervention are equally fraught. Russia would likely oppose any United Nations resolution on military action against Syria. That would leave the U.S. to cobble together another makeshift "coalition of the willing" that lacked official authorization by the international community.

The costs of doing nothing, however, are even less palatable. Since the end of World War I, chemical weapons have effectively been banned by international consensus. Tolerating their use against civilians in Syria would send a terrible signal not only about U.S. lack of resolve but of a weakening of the whole framework of arms control treaties built up over the last 100 years. Moreover, ignoring Syria's resort to chemical attacks would undoubtedly embolden North Korea and Iran in their pursuit of nuclear weapons.

Faced with no good alternatives, President Obama needs to make the best of a bad situation by clearly defining America's interest in Syria's civil war. The unhappy truth is that no one in Syria, including the government, can be trusted with these weapons. Ultimately, they must either be destroyed or removed from the country; that's the only way to ensure they won't fall into the wrong hands, but it would likely also require a massive military commitment.

We may not need to set that as our immediate goal, but we do need to ensure that the Assad regime recognizes that there are consequences for using chemical weapons. Mr. Obama says he wants to check and double check the reliability of the intelligence reports before considering how to respond. There's a window of time for officials to gather evidence, consult with allies and seek to have the UN weapons inspectors currently barred from Syria return to that country to confirm whether chemical weapons were used. After that, however, the administration's continued temporizing will begin to look like dithering. Mr. Obama must surely realize that his credibility and that of the entire U.S. government are now on the line and that what happens next depends on his willingness to back up his words with deeds.